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12-29-2011, 01:14 PM   #1
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K20D AF Adjustment advice?

I am having difficulty getting focused.... I am shooting my K20D with a DA*16-50. These AF Adjustment tests are shot at F2.8 at 50mm. I have attached three photos ranging from zero AF Adjustment to +5 and -5.

I cant seem to tell a difference? Should I be able too? I ran the test because I have taken a number of portaits and landscapes and have always felt that they were all out of focus. I thought I would try the test and see if it is me or the camera. My bet is me...

Any help would be appreciated! Thanks.

The photos go in order from Zero adjustment to +5 to -5. All other settings remained the same for each image.

Attached Images
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PENTAX K20D  Photo 
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PENTAX K20D  Photo 
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PENTAX K20D  Photo 
12-29-2011, 02:12 PM   #2
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What I see is a bit of a shifted focus plane, perhaps because of a lens misalignment or sensor misalignment.
To my eyes, the numbers in the back on the left side are more clearly in focus than the numbers on the right side.

Now for the focus test, are you returning the lens to infinity each time you make a change to the AF adjustment?
12-29-2011, 02:27 PM   #3
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Dump the chart, use distant real world target in daylight environment for AF calibration. Tune it at the wide end and reconfirm at the long end.
12-29-2011, 06:38 PM - 1 Like   #4
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QuoteOriginally posted by icywindow Quote
What I see is a bit of a shifted focus plane, perhaps because of a lens misalignment or sensor misalignment.
To my eyes, the numbers in the back on the left side are more clearly in focus than the numbers on the right side.

Now for the focus test, are you returning the lens to infinity each time you make a change to the AF adjustment?
Or, the camera isn't in exact alignment with the chart. Other than that there is a small change in where the focus falls that does seem to match the adjustment.

12-30-2011, 04:10 AM   #5
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Another reason as to why the left part isn't as sharp as the right part could be that the chart wasn't completely flat. A lens decentering issue wouldn't be uncommon with this lens model.

The first shot shows the best focus but shows very slight FF. Shouldn't cause trouble in practice, but you could try to use more drastic AF adjustment values to see whether that helps.

BTW, don't expect to be able to adjust both wide and long end of a zoom with just one value. Usually, the AF adjustment value will have to be a compromise for all focal lengths and focusing distances (see my "AF adjustment hints).
12-31-2011, 09:08 AM   #6
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What these pictures show is that the focus system is just fine - within normal tolerances that would not cause eeal world issues. So I,d next start looking at the actual images you are having trouble with and start figuring out what is really goong on - most likely, a matter of not selecting the focus point, or the focus sensor being to broad to allow pinpoint control.
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